Here's what happened: The district court excluded 404(b) evidence prior to trial. The Government later filed an exhibit list that included the excluded 404(b) evidence. Dugue moved to exclude that evidence from trial, a motion the court granted. During trial, while cross-examining Dugue, the prosecutor brought up the 404(b) evidence. Why? "The prosecutor claimed that, by raising his eyebrow and nodding his head, the district judge had given her permission to introduce the [excluded evidence.]" The district court granted Dugue's motion for a mistrial, but refused to bar a retrial because it found that the prosecutor had not intended to "goad" Dugue into moving for the mistrial.

Dugue appealed, arguing that if it looks, walks, and quacks like a duck, it's a duck:

He alleges that “[w]here a Government attorney acts with reckless disregard for the Orders of the Court, under circumstances where only a mistrial can cure the resultant prejudice, the intent to cause a mistrial can be inferred.” This court has never adopted such a per se rule and we question whether such a rule would be sufficient to show that the district court clearly erred. Instead, we have followed the Supreme Court’s ruling in [Oregon v.] Kennedy[, 456 U.S. 667 (1982)].

In Kennedy, the Court made it clear that prosecutorial misconduct alone is not sufficient for a retrial to result in a double jeopardy violation: “Prosecutorial conduct that might be viewed as harassment or overreaching, even if sufficient to justify a mistrial on defendant’s motion, therefore, does not bar retrial absent intent on the part of the prosecutor to subvert the protections afforded by the Double Jeopardy Clause.” Retrial is not barred even where the prosecution engages in “intentional misconduct that seriously prejudices the defendant.” Once the court determines that the prosecutor’s conduct was not intended to terminate the trial, “that is the end of the matter for purposes of the Double Jeopardy Clause of the Fifth Amendment. . . .”

United States v. Wharton, 320 F.3d 526, 531-32 (5th Cir. 2003) (internal citations omitted). For Dugue to obtain retrial, he would need to prove that [the prosecutor's reference to the excluded evidence] was intended to cause a mistrial—a factual determination.

The court went on to hold that the district court's factual determination to the contrary was not clear error, so the retrial is not barred. There was the obligatory scolding, as well:

The prosecutor displayed overreaching and unprofessional conduct in ignoring the district court’s two orders not to discuss the [excluded evidence]. Her excuse, that the judge’s head nod in response to her raised eyebrow implied permission to introduce previously excluded evidence, is certainly unacceptable. . . . The prosecutor’s improper behavior offers a reminder that attorneys should hew closely to the orders excluding evidence and seek clear permission when they are approaching those topics at a later point in trial.